During the fabrication of semiconductor integrated circuits and other devices, it is often desirable to apply an electrical probe to the contact pads of the chip in order to test the circuit. This probing is preferably done after solder bumps have been formed on the pads in order to prevent damage to the pads that can result in leakage. Normally, after only a few touchdowns, the contact resistance between the probe and the bump increases significantly and is very unstable, resulting in erroneous electrical measurements. A similar problem may exist even without solder when aluminum pads are used, since aluminum oxide tends to build up on the probes.
This contact resistance problem has traditionally been solved, in the case of solder bumps containing lead, by frequent cleaning of the probe tip using an abrasive surface. The probe tips are scrubbed across the surface and the solder build-up is sanded away. This process can be time consuming. Further, when lead-free solder bumps are employed, the cleaning frequency and aggressiveness are increased significantly for the cleaning to be effective. In fact, cleaning is required so often that the test throughput is severely curtailed. Also, the probe card wears out more quickly resulting in a higher cost for the tests.
It is, therefore, desirable to provide a method of electrical testing which does not require frequent cleaning of the test probes.